This invention relates to fluid displacement apparatus, and in particular, to fluid compressor units of the scroll type.
Scroll type fluid displacement apparatus are well known in the prior art. For example, U.S. Pat. No. 801,812 discloses a device including two scroll members each having an end plate and a spiroidal or involute spiral element. The scroll members are maintained angularly and radially offset so that both spiral elements interfit and meet at a plurality of line contacts between the spiral curved surfaces, to thereby seal off and define at least one pair of fluid pockets. The relative orbital motion of these scroll members shifts the line contacts along the spiral curved surfaces and, therefore, changes the volume in the fluid pockets. The volume of the fluid pockets increases or decreases depending on the direction of orbital motion. Therefore, the scroll type fluid displacement apparatus is applicable to compress, expand or pump fluids.
The scroll type fluid displacement apparatus is suitable for use as a refrigerant compressor for an automobile air conditioner. Generally, it is desirable that the compressor should be compact and light in weight so that it can fit comfortably within the engine compartment and not add appreciably to vehicle weight. However, the compressor for an automobile air conditioner is generally connected to a magnetic clutch at the housing and outer portion of the drive shaft to transmit the rotary output of the engine to the drive shaft of the compressor. The weight of the magnetic clutch is therefore added to the weight of the compressor unit, to thereby increase the total weight of the compressor unit. A pulley which is included in the magnetic clutch is rotatably supported on a sleeve portion of the compressor by a bearing, and a magnetic coil is disposed within an annular cavity of the pulley. The radial diameter of the compressor is therefore restricted by the diameter of the bearing.
A scroll type displacement apparatus is capable of operating at high speed, because the relative rubbing speed between the scroll members can be made quite low, since the orbiting scroll member is driven at a very small orbital radius. However, the diameter of the pulley is restricted by the diameter of the bearing or magnetic coil; therefore, the drive ratio is limited.
When a compliant "vertical crank" mechanism (which changes the orbital radius of orbital motion as required) is used as a driving mechanism for the orbiting scroll member, the orbiting scroll member is rotatably supported on the driving mechanism, allowing the orbiting scroll member to swing around the driving mechanism when the compressor is not in operation. In this case, the swinging scroll member can interfere with the fixed scroll member, which may cause vibration of the engine during driving a car, and either or both of the scroll members may be damaged.